Methods of making integrated circuits including air gaps around interconnect structures

ABSTRACT

A method of making an integrated circuit includes forming an interconnect structure in an opening in a dielectric layer. The method further includes forming an air gap between the dielectric layer and the interconnect structure, where a first liner layer along a bottom portion of a sidewall of the opening of the dielectric layer is under the air gap, and a top portion of the first liner layer is below a lowest portion of the air gap.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No. 13/858,639, filed Apr. 8, 2013, which is a continuation of U.S. patent application Ser. No. 12/718,616, filed Mar. 5, 2010, which are incorporated herein by reference in their entireties.

RELATED APPLICATIONS

The present application is related to U.S. application Ser. No. 12/132,233, entitled “SEMICONDUCTOR INTERCONNECT AIR GAP FORMATION PROCESS,” filed on Jun. 3, 2008, now U.S. Pat. No. 7,754,601 and U.S. Provisional Application No. 61/176,002, entitled “INTEGRATED CIRCUITS INCLUDING ILD STRUCTURE, SYSTEMS, AND FABRICATION METHODS THEREOF,” filed on May 5, 2009, which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to the field of semiconductor devices, and more particularly, to methods of making integrated circuits including air gaps around interconnect structures.

BACKGROUND

Semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.

In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling-down also produces a relatively high power dissipation value, which may be addressed by using low power dissipation devices such as complementary metal-oxide-semiconductor (CMOS) devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic cross-sectional view of a first exemplary integrated circuit including at least one air gap that is disposed around an interconnect structure.

FIG. 2 is a schematic cross-sectional view of a second exemplary integrated circuit including at least one air gap that is disposed around an interconnect structure.

FIG. 3 is a schematic cross-sectional view of a third exemplary integrated circuit including at least one air gap that is disposed around an interconnect structure.

FIGS. 4A-4E are schematic cross-sectional views illustrating an exemplary method of forming an exemplary integrated circuit.

FIG. 5 is a schematic drawing illustrating a system including an exemplary integrated circuit disposed over a substrate board.

DETAILED DESCRIPTION

As mentioned above, the trend in the semiconductor industry is towards the miniaturization or scaling of integrated circuits, in order to provide smaller ICs and improve performance, such as increased speed and decreased power consumption. Low dielectric constant (low-k) dielectrics have been proposed to reduce parasitic capacitances between metallic lines and/or metallic layers. The parasitic capacitances can increase a resistance-capacitance (RC) time delay and, therefore, slow down the operation speed of the integrated circuit.

It is understood that the following disclosure provides many different embodiments, or examples. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a feature on, connected to, and/or coupled to another feature in the present disclosure that follows may include embodiments in which the features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the features, such that the features may not be in direct contact. In addition, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one features relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

An embodiment of the present application provides an integrated circuit including at least one air gap around an interconnect structure. The integrated circuit includes a dielectric layer disposed over a substrate. The dielectric layer includes at least one opening therein. An interconnect structure is disposed at least partially in the at least one opening. At least one first liner material is disposed around the interconnect structure. At least one air gap is disposed between the dielectric layer and the at least one first liner material. At least one second liner material is disposed below the at least one air gap and between the dielectric layer and the at least one first liner material. By forming the air gap around the interconnect structure, a parasitic capacitance between the interconnect structure and a neighboring interconnect structure can be desirably reduced. The resistance-capacitance (RC) time delay can be improved.

FIG. 1 is a schematic cross-sectional view of a first exemplary integrated circuit including at least one air gap that is disposed around an interconnect structure. In FIG. 1, an integrated circuit 100 can include at least one dielectric layer, such as a dielectric layer 110, disposed over a substrate 101. In some embodiments, the substrate 101 can include active regions, source/drain regions of transistors, interconnection structures, such as contacts, vias, and metallic lines, devices, circuits, other semiconductor structures, or any combinations thereof.

In some embodiments, the substrate 101 can include an elementary semiconductor including silicon or germanium in crystal, polycrystalline, or an amorphous structure; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlinAs, AlGaAs, GaInAs, GaInP, and GaInAsP; any other suitable material; or combinations thereof. In one embodiment, the alloy semiconductor substrate may have a gradient SiGe feature in which the Si and Ge composition change from one ratio at one location to another ratio at another location of the gradient SiGe feature. In another embodiment, the gradient SiGe feature is formed over a silicon substrate. In yet another embodiment, the gradient SiGe feature is strained. Furthermore, the semiconductor substrate may be a semiconductor on insulator, such as a silicon on insulator (SOI), or a thin film transistor (TFT). In some examples, the semiconductor substrate may include a doped epitaxial layer or a buried layer. In some other examples, the compound semiconductor substrate may have a multilayer structure, or the substrate may include a multilayer compound semiconductor structure.

Referring again to FIG. 1, in some embodiments, the dielectric layer 110 may include at least one material, such as carbon-containing silicon oxide, carbon-containing silicon nitride, carbon-containing silicon oxynitride, carbon-containing low-k dielectric material, ultra low-k dielectric material, or any combinations thereof. In some embodiments, the dielectric layer 110 can be made of a low-k dielectric material having a dielectric constant k less than or equal to 3, such as Black Diamond® available from Applied Materials, Incorporated®. In some other embodiments, the dielectric layer 110 may be made of such as, without limitation, fluorinated silicate glass (FSG) or undoped silicate glass (USG). In still other embodiments, the material selected for dielectric layer 110 can be susceptible to etching by anisotropic dry gas plasma etching chemistries.

In some embodiments, additional dielectric layer can be formed between the dielectric layer 110 and the substrate 101. For example, an etch stop layer (ESL) 105 can be formed over the substrate 101. The ESL 105 can include materials such as silicon nitride, silicon oxynitride, a silicon-carbon based material, such as silicon carbide (SiC), carbon-doped silicon oxide, or any combinations thereof.

Referring to FIG. 1, the integrated circuit 100 can include at least one interconnect structure, such as interconnect structures 120 and 121. Each of the interconnect structures 120 and 121 can be disposed in openings (not labeled) of the dielectric layer 110. The interconnect structures 120 and 121 can include at least one material such as copper (Cu), tungsten (W), aluminum (Al), Al/Cu, other conductive materials, or any combinations thereof.

In some embodiments, at least one barrier layer (not shown) can be disposed adjacent the sidewalls and/or bottoms of the interconnect structures 120 and 121. The barrier layer can include at least one material such as tantalum (Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN), tantalum silicon nitride (TaSiN), W, tungsten nitride (WN), other barrier layer materials, or any combinations thereof. The barrier layer can be formed, for example, by a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, a plasma enhanced CVD (PECVD) process, an atomic layer deposition (ALD) process, other deposition processes, or any combinations thereof.

Referring to FIG. 1, liner materials 130 a and 130 b can be disposed around the interconnect structures 120 and 121, respectively. In some embodiments, the liner materials 130 a and 130 b can include at least one material such as silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), silicon carbide (SiC), other liner materials, or any combinations thereof.

Referring again to FIG. 1, at least one air gap, e.g., air gaps 140 a and 140 b, can be disposed between the dielectric layer 110 and the interconnect structures 120 and 121, respectively. Though the cross-sectional view of FIG. 1 shows two air gaps 140 aeach being disposed adjacent the opposite sidewall of the dielectric layer 110, the scope of this application is not limited thereto. In some embodiments from a top view of the integrated circuit 100, the air gaps 140 a are configured around the pattern of the interconnect structure 120. In the top view of the integrated circuit 100, a single air gap 140 a is disposed around the interconnect structure 120.

Due to the air gaps 140 a and 140 b, the equivalent dielectric constant between the interconnect structures 120 and 121 can be reduced. The parasitic capacitance between the interconnect structures 120 and 121 can be reduced, too. The RC time delay resulting from the parasitic capacitance can be desirably improved. In some embodiments, each of the air gaps 140 a and 140 b can have a width “W” and the interconnect structure 120 and 121 can have a pitch width “P”. In some embodiments, a ratio of the width “W” to the pitch width “P” can be in a range from about 1/15 to about ¼.

Referring to FIG. 1, at least one liner material, such as liner materials 150 a, can be disposed below the air gaps 140 a and between the dielectric layer 110 and the liner materials 130 a. In some embodiments, the interconnect structure 120 is a damascene structure, e.g., a single damascene structure or a dual damascene structure. The interconnect structure 120 can include a metallic line 120 a and a via region 120 b. The liner materials 150 a can be disposed around the via region 120 b.

In some embodiments, each of the liner materials 130 a and 150 a can be made of at least one material, such as silicon oxide, silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), silicon carbide (SiC), other liner materials, or any combinations thereof. In some embodiments, the liner material 130 a and the liner material 150 a are made of different materials or different combination of materials. For example, the liner material 130 a can be made of at least one material, such as silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), silicon carbide (SiC), other liner materials, or any combinations thereof. The liner materials 150 a can be made of at least one material, such as silicon oxide, substantially carbon-free silicon oxide, other materials that have an etch selectivity to the liner materials 130 a of about 10:1 or more, or any combinations thereof. In other embodiments, an etch selectivity of the liner materials 150 a to the dielectric layer 110 can be about 10:1 or more.

It is noted that the integrated circuit 100 including the air gaps 140 a and 140 b described above in conjunction with FIG. 1 is merely exemplary. In some embodiments, at least one of an ESL, a dielectric layer, via plugs, metallic regions, metallic lines, passivation layers, other semiconductor structures (not shown), or any combinations thereof can be formed over the structure shown in FIG. 1.

The ESL (not shown) can include at least one material, such as silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbide, other dielectric material, or any combinations thereof. The dielectric layer (not shown) may include materials such as silicon oxide, silicon nitride, silicon oxynitride, low-k dielectric material, ultra low-k dielectric material, or any combinations thereof. The via plugs, metallic regions, and/or metallic lines (not shown) can include materials such as tungsten, aluminum, copper, titanium, tantalum, titanium nitride, tantalum nitride, nickel silicide, cobalt silicide, other proper conductive materials, and/or combinations thereof.

FIG. 2 is a schematic cross-sectional view of a second exemplary integrated circuit including at least one air gap disposed around an interconnect structure. Items of FIG. 2 that are the same items in FIG. 1 are indicated by the same reference numerals, increased by 100. For example, as depicted in FIG. 2, an integrated circuit 200 includes an etch stop layer (ESL) 205 and a dielectric layer 210 over a substrate 201, interconnect structures 220 and 221, liner materials 230 a and 230 b around the interconnect structures 220 and 221, and air gaps 240 a and 240 b between the dielectric layer 210 and the interconnect structures 220 and 221, respectively. The interconnect structure 220 includes a metallic line 220 a and a via region 220 b. The liner materials 250 a are around the via region 220 b. In FIG. 2, at least one damage layer, e.g., damage layers 260, can be disposed between liner materials 250 a and the dielectric layer 210. In some embodiments, the damage layers 260 can include at least one material, such as silicon oxide, substantially carbon-free silicon oxide, other SiOH-containing dielectric materials, or any combinations thereof. In some other embodiments, the damage layers 260 can be formed by subjecting sidewalls of the dielectric layer 210 to an ashing gas, e.g., an oxygen ashing gas. Due to the ashing process, temporary, expendable oxidized sidewall portions of the dielectric layer 210 can be formed.

FIG. 3 is a schematic cross-sectional view of a third exemplary integrated circuit including at least one air gap disposed around an interconnect structure. Items of FIG. 3 that are the same items in FIG. 1 are indicated by the same reference numerals, increased by 200. For example, as depicted in FIG. 3, an integrated circuit 300 includes an etch stop layer (ESL) 305 and a dielectric layer 310 over a substrate 301, interconnect structures 320 and 321, liner materials 330 a and 330 b around the interconnect structures 320 and 321, and air gaps 340 a and 340 b between the dielectric layer 310 and the interconnect structures 320 and 321, respectively. The interconnect structure 320 includes a metallic line 320 a and a via region 320 b. The liner materials 350 a are around the via region 320 b. In FIG. 3, the integrated circuit 300 can include at least one liner material, e.g., liner materials 370 a and 370 b. Air gaps 340 a can be formed between the liner materials 330 a and 370 a and air gaps 340 b can be formed between the liner materials 330 b and 370 b. In some embodiments, the liner materials 370 a and 370 b can include at least one material such as silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), silicon carbide (SiC), or other liner materials to which an etch selectivity of the liner materials 350 a is about 10:1 or more.

FIGS. 4A-4E are schematic cross-sectional views illustrating an exemplary method of forming the exemplary integrated circuit 100 described above in conjunction with FIG. 1 according to some embodiments. Items of FIG. 4 that are the same items in FIG. 1 are indicated by the same reference numerals, increased by 300. In FIG. 4A, an etch stop layer (ESL) 405 of an integrated circuit 400 can be formed over a substrate 401. The ESL 405 can be formed, for example, by plasma enhanced chemical vapor deposition (PECVD), CVD, such as high-density plasma CVD (HDPCVD), atomic layer CVD (ALCVD), or the like.

Referring to FIG. 4A, a dielectric layer 410 can be formed over the ESL 405. The dielectric layer 410 may be formed, for example, by a CVD process, a PECVD process, a HDP CVD process, a HARP, a spin-coating process, another deposition process, or any combinations thereof. At least one opening, e.g., openings 415 a and 415 b, can be formed in the dielectric layer 410.

The opening 415 a can expose at least a portion of the ESL 405. In some embodiments, the openings 415 a and 415 b can be formed by defining a photoresist pattern (not shown) over a dielectric material that is deposited for forming the dielectric layer 410. A dry etch process uses the photoresist pattern as a mask to remove portions of the dielectric material for defining the openings 415 a and 415 b. The ESL 405 can protect the substrate 401 from being damaged by the dry etch process. After the openings 415 a and 415 b are formed, the photoresist pattern can be removed.

Referring to FIG. 4B, liner layers 450 and 430 can be sequentially formed over the dielectric layer 410. In some embodiments, the liner layers 450 and 430 can be substantially conformal over the dielectric layer 410. Each of the liner layers 450 and 430 can be formed, for example, by atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD), other suitable deposition processes, or any combinations thereof.

Referring to FIG. 4C, a removing process 425 can remove portions of the liner layers 430 and 450 (shown in FIG. 4B) for defining liner materials 430 a-430 b and liner layers 451-452 adjacent sidewalls of the dielectric layer 410. In some embodiments, the removing process 425 can remove the top portions of the liner layers 430 and 450 that are over the top surface 410 a of the dielectric layer 410 and bottom portions of the liner layers 430 and 450. In some embodiments, the removing process 425 can also remove a portion of the ESL 405 so as to expose a portion of the surface of the substrate 401. The removing process 425 can include a dry etch process, a dry plasma etch process, an ashing plasma process, a wet etch process, or any combinations thereof.

Referring to FIG. 4D, interconnect structures 420 and 421 can be formed in the openings 415 a and 415 b, respectively. In some embodiments, a metallic layer that is deposited for forming the interconnect structures 420 and 421 can be formed in the openings 415 a and 415 b and over the dielectric layer 410. The metallic layer can include at least one material, such as copper, tungsten, Al, Al/Cu, other conductive materials, or combinations thereof and can be deposited by a CVD, PVD, ALD, electroplating method, and/or other process. The metallic layer deposited over the dielectric layer 410 can be removed by a chemical mechanical polish (CMP) process (not shown) for defining the interconnect structures 420 and 421. After the CMP process, the top surfaces of the liner materials 430 a-430 b and the liner layers 451-452 can be substantially level with the top surfaces of the interconnect structures 420 and 421. The top surfaces (not labeled) of the liner materials 430 a-430 b and the liner layers 451-452 are exposed as shown in FIG. 4D.

Referring to FIG. 4E, a removing process 435 can substantially remove all the liner layers 452 and remove portions of the liner layers 451 (shown in FIG. 4D) for forming air gaps 440 b and 440 a, respectively. The remaining portions of the liner layers 451, i.e., the liner materials 450 a, can be defined below the air gaps 440 a. In some embodiments, chemicals and/or compositions in a liquid or gaseous state may be used to dissolve the liner layers 452 and the portions of the liner layers 451 through their exposed top surfaces. The chemicals and/or compositions selected do not substantially etch or damage the dielectric material 410 and the liner materials 430 a and 430 b to a degree that might adversely affect the reliability of the integrated circuit 400. In other embodiments, the removing process 435 can have an etch selectivity of the liner layers 451-452 to the dielectric material 410 of about 10:1 or more. In still other embodiments, the removing process 435 can also have an etch selectivity of the liner layers 451-452 to the liner materials 430 a-430 b of about 10:1 or more.

In some embodiments, a wet etching may be used to form the air gaps 440 a and 440 b by dipping the integrated circuit 400 in a dilute hydrofluoric acid (HF) based solution that reacts with and dissolves the liner layers 452 and the portions of the liner layers 451. The HF acid-based solution may be relatively dilute, which in some exemplary embodiments may contain 5% or less of HF acid. In some other embodiments, the HF acid-based solution may contain approximately 1% concentration of HF acid. Such concentrations of HF acid may be used without significant adverse effects on the dielectric material 410 and the liner materials 430 a-430 b. Representative dip times may be from a few seconds to about 60 minutes depending on the concentration of the HF solution used, which affects the aggressiveness of the solution and material etching rates. In some embodiments, the chemicals and/or compositions selected do not substantially damage the interconnect structures 420 and 421. It will be appreciated that other chemicals and/or compositions, and dry etching techniques may be used to dissolve and remove the liner layers 452 and the portions of the liner layers 451 to form the air gaps 430 b and 430 a, respectively.

As note, the thickness of the liner layer 450 can be substantially conformal over the dielectric layer 410. Since the air gaps 430 b and 430 a are formed by removing the liner layers 452 and the portions of the liner layers 451, respectively, the width of the air gaps 430 a and 430 b can be desirably controlled. The width of the air gaps 430 a and 430 b can be substantially equal to each other. By forming the air gaps 430 a and 430 b having the substantially uniform width, the parasitic capacitance between interconnect structures can be desirably controlled. Desired uniform electrical performances of the integrated circuit 400 can be achieved.

It is noted that the method of forming the integrated circuit 400 described above in conjunction with FIGS. 4A-4E is merely exemplary. In some embodiments, at least one of an ESL, a dielectric material, via plugs, metallic regions, and/or metallic lines (not shown) can be formed over the structure shown in FIG. 1. The ESL can be formed, for example, by plasma enhanced chemical vapor deposition (PECVD), CVD process, such as high-density plasma CVD (HDPCVD), atomic layer CVD (ALCVD), or the like. The via plugs, metallic regions, and/or metallic lines can be formed, for example, by at least one of deposition processes, photolithographic processes, etch processes, CMP processes, cleaning process, or any combinations thereof.

In some embodiments, the method described above in conjunction with FIGS. 4A-4E can be modified to form the integrated circuit 200 described above in conjunction with FIG. 2. In this embodiment, the sidewalls of the dielectric layer 410 (shown in FIG. 4A) can be subjected to a dry ashing process (not shown). Damage portions that are configured for forming the damage layers (described in conjunction with FIG. 2) can be formed on the exposed sidewalls of the dielectric layer 410. The dielectric layer 410 can be treated by the ashing gas and damaged or oxidized by reaction of the oxygen ashing gas plasma with the dielectric material 410 to produce a temporary, expendable damage layers on the sidewalls of the dielectric layer 410. The liner layers 450 and 430 (shown in FIG. 4B) are then sequentially formed over the damage layers. Each of the damage layers is formed between the dielectric layer 410 and the liner layer 450.

In some embodiments, the damage layers may contain SiOH resulting from a chemical reaction of the dielectric layer 410 with an oxygen plasma ashing gas. The length of time that the sidewalls of the dielectric layer 410 are exposed to the oxygen plasma ashing gas, thereby allowing the oxygen plasma ashing gas to diffuse into the dielectric layer 410, can be used to control the depth of the damage layers.

While removing the liner layers 452 and the portions of the liner layers 451, the removing process 435 can remove portions of the damage portions so as to define the damage layers 260 as shown in FIG. 2. As noted, the damage layers can be formed between the liner materials 450 a and the dielectric layer 410.

In some other embodiments, the method described above in conjunction with FIGS. 4A-4E can be modified to form the integrated circuit 300 described above in conjunction with FIG. 3. In this embodiment, another liner layer (that is deposited for forming the liner materials 370 a and 370 b shown in FIG. 3) can be formed and substantially conformal over the liner layer 430 (shown in FIG. 4B). As noted, the liner materials 450 a and 450 b can have an etch selectivity to the liner layer of about 10:1 or more. The removing process 435 can remove portions of the liner materials 450 a and the liner materials 450 b, forming the air gaps between to liner materials. The air gaps having a substantially uniform width can be achieved.

FIG. 5 is a schematic drawing illustrating a system including an exemplary integrated circuit disposed over a substrate board. In FIG. 5, a system 500 can include an integrated circuit 502 disposed over substrate board 501. The substrate board 501 can include a printed circuit board (PCB), a printed wiring board and/or other carrier that is capable of carrying an integrated circuit. The integrated circuit 502 can be similar to the integrated circuit 100, 200, or 300 described above in conjunction with FIGS. 1-3, respectively. The integrated circuit 502 can be electrically coupled with the substrate board 501. In some embodiments, the integrated circuit 502 can be electrically coupled with the substrate board 501 through bumps 505. In some other embodiments, the integrated circuit 502 can be electrically coupled with the substrate board 501 through wire bonding. The system 500 can be part of an electronic system such as computers, wireless communication devices, computer-related peripherals, entertainment devices, or the like.

In some embodiments, the system 500 including the integrated circuit 502 can provides an entire system in one IC, so-called system on a chip (SOC) or system on integrated circuit (SOIC) devices. These SOC devices may provide, for example, all of the circuitry needed to implement a cell phone, personal data assistant (PDA), digital VCR, digital camcorder, digital camera, MP3 player, or the like in a single system.

One aspect of this description relates to a method of making an integrated circuit including forming an interconnect structure in an opening in a dielectric layer. The method further includes forming an air gap between the dielectric layer and the interconnect structure, where a first liner layer along a bottom portion of a sidewall of the opening of the dielectric layer is under the air gap, and a top portion of the first liner layer is below a lowest portion of the air gap.

Another aspect of this description relates to a method of making an integrated circuit including forming an interconnect structure in an opening in a dielectric layer. The method further includes forming an air gap between the dielectric layer and the interconnect structure, where a first liner layer along a bottom portion of a sidewall of the opening of the dielectric layer is under the air gap. Additionally, the method includes forming a damage layer between the first liner layer and the dielectric layer.

Still another aspect of this description relates to a method of making an integrated circuit including forming a first interconnect structure in a first opening in a dielectric layer, wherein the first opening has a first depth. The method further includes forming a second interconnect structure in a second opening in the dielectric layer separate from the first opening, where the second opening has a second depth different from the first depth. Additionally, the method includes forming a first air gap between the dielectric layer and the first interconnect structure, where a first liner layer along a bottom portion of a sidewall of the first opening is under the first air gap. Furthermore, the method includes forming a second air gap between the dielectric layer and the second interconnect structure, wherein at least one of the first air gap or the second air gap has a constant width.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of making an integrated circuit, the method comprising: forming an interconnect structure in an opening in a dielectric layer; forming an air gap between the dielectric layer and the interconnect structure, wherein a first liner layer along a bottom portion of a sidewall of the opening of the dielectric layer is under the air gap, and wherein a top portion of the first liner layer is below a lowest portion of the air gap.
 2. The method of claim 1, wherein the forming the air gap comprises: forming a second liner layer around the interconnect structure; forming the first liner layer between the dielectric layer and the second liner layer; and removing a portion of the first liner layer.
 3. The method of claim 2, wherein a ratio of an etch selectivity of the first liner layer to an etch selectivity of the second liner layer is 10:1 or more and a ratio of the etch selectivity of the first liner layer to an etch selectivity of the dielectric layer is 10:1 or more.
 4. The method of claim 1, wherein forming the air gap comprises forming the air gap having a width ranging from one-fifteenth of a pitch width of the interconnect structure to one-fourth of the pitch width of the interconnect structure.
 5. The method of claim 1, wherein forming the interconnect structure comprises forming the interconnect structure comprises at least one of copper, tungsten, or aluminum.
 6. A method of making an integrated circuit, the method comprising: forming an interconnect structure in an opening in a dielectric layer; forming an air gap between the dielectric layer and the interconnect structure, wherein a first liner layer along a bottom portion of a sidewall of the opening of the dielectric layer is under the air gap, and forming a damage layer between the first liner layer and the dielectric layer.
 7. The method of claim 6, wherein the forming the damage layer comprises oxygen ashing an exposed portion of a sidewall of the opening in the dielectric layer.
 8. The method of claim 6, wherein the forming the air gap comprises: forming a second liner layer around the interconnect structure; forming the first liner layer between the dielectric layer and the second liner layer; and removing a portion of the first liner layer so as to form the air gap over the first liner layer.
 9. The method of claim 8, wherein a ratio of an etch selectivity of the first liner layer to an etch selectivity of the second liner layer is 10:1 or more and a ratio of the etch selectivity of the first liner layer to an etch selectivity of the dielectric layer is 10:1 or more.
 10. The method of claim 6, wherein forming the interconnect structure comprises forming the interconnect structure comprises at least one of copper, tungsten, or aluminum.
 11. The method of claim 6, wherein forming the air gap comprises forming the first liner layer comprising at least one of silicon oxide, silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), or silicon carbide (SiC).
 12. The method of claim 6, further comprising forming a barrier layer adjacent to sidewalls of the interconnect structure.
 13. The method of claim 12, wherein forming the barrier layer comprises forming the barrier layer comprising at least one of tantalum, titanium, tantalum nitride, titanium nitride, tantalum silicon nitride, tungsten, or tungsten nitride.
 14. A method of making an integrated circuit, the method comprising: forming a first interconnect structure in a first opening in a dielectric layer, wherein the first opening has a first depth; forming a second interconnect structure in a second opening in the dielectric layer, wherein the second opening is separate from the first opening, and the second opening has a second depth different from the first depth; forming a first air gap between the dielectric layer and the first interconnect structure, wherein a first liner layer along a bottom portion of a sidewall of the first opening is under the first air gap; and forming a second air gap between the dielectric layer and the second interconnect structure; wherein at least one of the first air gap or the second air gap has a constant width.
 15. The method of claim 14 further comprising, forming a barrier layer adjacent to sidewalls of the first interconnect structure.
 16. The method of claim 15, wherein forming the barrier layer comprises forming the barrier layer comprising at least one of tantalum, titanium, tantalum nitride, titanium nitride, tantalum silicon nitride, tungsten, or tungsten nitride.
 17. The method of claim 14, wherein forming the first interconnect structure comprises forming the first interconnect structure comprising at least one of copper, tungsten or aluminum, and forming the second interconnect structure comprises forming the second interconnect structure comprising at least one of copper, tungsten, or aluminum.
 18. The method of claim 14, wherein forming the first air gap comprises forming the first liner layer comprising at least one of silicon oxide, silicon nitride, silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbon nitride (SiCN), silicon carbon oxynitride (SiCON), or silicon carbide (SiC).
 19. The method of claim 14, wherein the forming the first air gap comprises: forming a second liner layer around the first interconnect structure; forming the first liner layer between the dielectric layer and the second liner layer; and removing a portion of the first liner layer so as to form the air gap over the first liner layer.
 20. The method of claim 19, wherein a ratio of an etch selectivity of the first liner layer to an etch selectivity of the second liner layer is 10:1 or more and a ratio of the etch selectivity of the first liner layer to an etch selectivity of the dielectric layer is 10:1 or more. 